bug#15998: 24.3; forward-sexp (scan-sexps) doesn't do well with some SEXPs

[Noam Postavsky]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> But do we want to implement a brand new forward-sexp just for Emacs Lisp?
>
> No, but I think syntax-propertize can take care of those things.

The patch below seems to work, no new sexp movement commands needed?

>From 463f98c55ff7d6bde576a9538d3ae3a33a576cf5 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Sat, 6 Jul 2019 21:55:03 -0400
Subject: [PATCH] Handle elisp #-syntax better (Bug#15998)

* elisp-mode.el (elisp-mode-syntax-propertize): New function.
(emacs-lisp-mode): Set it as syntax-propertize-function.
---
 lisp/progmodes/elisp-mode.el | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/lisp/progmodes/elisp-mode.el b/lisp/progmodes/elisp-mode.el
index cb1b17b447..c86277a309 100644
--- a/lisp/progmodes/elisp-mode.el
+++ b/lisp/progmodes/elisp-mode.el
@@ -213,6 +213,20 @@ emacs-lisp-macroexpand
       (if (bolp) (delete-char -1))
       (indent-region start (point)))))
 
+(defun elisp-mode-syntax-propertize (start end)
+  (goto-char start)
+  (funcall
+   (syntax-propertize-rules
+    ("##" (0 (unless (nth 8 (syntax-ppss)) ; Empty symbol.
+               (string-to-syntax "_"))))
+    ((rx "#" (or (seq (group-n 1 (+ digit) "="))     ; Object label.
+                 (seq (group-n 1 "&" (+ digit)) ?\") ; Bool-vector.
+                 (seq (group-n 1 "s") "(")           ; Record.
+                 (seq (group-n 1 (+ "^")) "[")))     ; Char-table.
+     (1 (unless (save-excursion (nth 8 (syntax-ppss (match-beginning 0))))
+          (string-to-syntax "'")))))
+   start end))
+
 (defcustom emacs-lisp-mode-hook nil
   "Hook run when entering Emacs Lisp mode."
   :options '(eldoc-mode imenu-add-menubar-index checkdoc-minor-mode)
@@ -242,6 +256,7 @@ emacs-lisp-mode
                 #'elisp-eldoc-documentation-function)
   (add-hook 'xref-backend-functions #'elisp--xref-backend nil t)
   (setq-local project-vc-external-roots-function #'elisp-load-path-roots)
+  (setq-local syntax-propertize-function #'elisp-mode-syntax-propertize)
   (add-hook 'completion-at-point-functions
             #'elisp-completion-at-point nil 'local)
   (add-hook 'flymake-diagnostic-functions #'elisp-flymake-checkdoc nil t)
-- 
2.11.0